NC State Scientist Devises New, More Rapid Gene Silencing Technique

Date:

June 1, 1999

Source:

North Carolina State University

Summary:

Crops with increased resistance to drought and disease, soybeans with more protein and vegetables with more vitamins are some of the potential benefits that may result from a new gene silencing technology developed at North Carolina State University.

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Crops with increased resistance to drought and disease, soybeans with more protein and vegetables with more vitamins are some of the potential benefits that may result from a new gene silencing technology developed at North Carolina State University.

The technology, created by Dr. Dominique "Niki" Robertson, associate professor of botany, allows researchers to inhibit the expression of a selected gene in a plant and then study how the plant grows without it -- ultimately helping them identify what that gene's function is.

Robertson's method represents a huge improvement over existing gene silencing technologies because it allows for 100 percent silencing in as few as two to four weeks. Other methods provide only 1 percent to 10 percent silencing in three to six months.

The new technology also can be used to silence two genes at once. "Sometimes more than one gene controls a pathway or process," Robertson says. "By silencing multiple genes, we can determine if they act alone or in concert."

"There is so much we could potentially do by determining the function of genes. If, for instance, we (can identify) the genes that determine plant growth, we could get plants to go through another round of cell divisions and double the biomass, increasing the plant's food output," she says.

NC State has applied for a patent on Robertson's technique. Monsanto Co. has an option to the technology and is a principal sponsor of Robertson's ongoing research.

Using the technology, scientists insert fragments of a specific plant gene into a Gemini-type DNA virus, a class of viruses that attack plants. An intact plant is then inoculated with the virus through a process called microprojectile bombardment, which uses small particles of gold to insert the DNA into the plant. The virus then moves the gene through the plant from bottom to top. The presence of the extra gene fragment in the plant cells causes silencing of similar genes in the plant chromosomes by blocking their expression.

An advantage of the new method is that it allows scientists to use smaller gene fragments than ever before possible. Many plant genes are more than 1,000 bases long, making it impossible to insert the entire gene into the DNA virus. However, Robertson's process has been used successfully to silence genes in plants using DNA fragments as small as 100 bases long.

The process was first tested successfully on a gene known to be involved in the production of chlorophyll, which gives plants color. After being inoculated with the gene-carrying DNA virus, some of the test plants produced variegated leaves. One plant exhibited entirely white leaves in its upper growth.

Robertson also tested the process on a gene thought to be required for viral DNA replication in plants. Silencing that gene prevented viral infection in the test plant. "Now we know that the gene is needed for viral DNA replication," she says.

She hopes her research will lead to a better understanding of the Gemini-type DNA viruses that attack plants. For instance, the cassava, a staple food in much of Africa, is highly susceptible to a similar virus. The NC State process may help researchers develop a form of cassava that is resistant to the virus.

Robertson's research is part of an emerging new scientific field called functional genomics, in which scientists aim to learn how genes are expressed in plants and animals. Other genetics research, such as the Human Genome Project, is generating huge amounts of data about DNA sequencing, Robertson says, but it doesn't reveal what the functions of the mapped genes are. That's where functional genomics comes in.

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